Static shield for oil circuit breaker interrupters



July 7, 1970 E. B. RIETZ 3,519,774

STATIC SHIELD FOR OIL CIRCUIT BREAKER INTERRUPTERS Filed Jan. 7, 1966 a v 3 Sheets-Sheet 1 ENTOR. 14141 6 ?/7Z 2 f j Gaza JbFF-A/ E. B. RIETZ July 7, 1970 STATIC SHIELD FOR OIL CIRCUIT BREAKER INTERRUPTERS Filed Jan. 7, 1966 3 Sheets-Sheet 2 INVENTOR. fflfl 5. 6 /67 Z y 7-, 1970 E. B. RIETZ 3,519,774

STATIC SHIELD FOR OIL CIRCUIT BREAKER INTERRUPTERS Filed Jan. 7, 1966 5 Sheets-Sheet .5

- INVENTOR. ffl/fd 5 i/i/Z United States Patent 3,519,774 STATIC SHIELD FOR OIL CIRCUIT BREAKER INTERRUPTERS Earl B. Rietz, La Canada, Califi, assignor, by mesne assignments, to I-T-E Imperial Corporation, Philadelphia, Pa, a corporation of Delaware Filed Jan. 7, 1966, Ser. No. 519,348 Int. Cl. H01h 33/68 US. Cl. 200150 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a novel shield structure for oil circuit breaker interrupters, and more specifically relates to a novel static shield connected around the bottom of the interrupter tube which is electrically connected to the potential of the resistor contacts.

Oil circuit breakers are well known and commonly comprise an interrupter immersed in oil where the interrupter is an elongated tube having main stationary contacts at the upper end thereof which receive a movable bayone contact which enters the tube. A shunting resistor is then commonly connected in parallel with the interrupter contacts with one end of the resistor permanently connected to the upper interrupter adapter connected to the interrupter stationary contacts. The other resistor terminal is then connected to resistor contacts which are normally contained at the bottom of the interrupter assembly and make sliding electrical contact on the moving bayonet-type contact or contact rod.

The connection of the resistor to these contacts will bring the line potential to the lower section of the interrupter. Therefore, when the main contacts are open, there will be a potential across the 'gap between resistor contacts and the open movable contact rod.

Since the resistor contacts act as a termnial, there will be an electrostatic field of high gradient emanating from these contacts. This field will then stress the insulation components immediately below the resistor contacts, particularly in construction of the type described in copending application Ser. No. 439,304, filed Mar. 12, 1965, entitled Interrupter Structure for Oil Circuit Breakers, in the name of Rietz et al., and assigned to the assignee of the instant invention, and particularly the insulation throat bushing and the surfaces between the throat bushing and the lower end of the insulation interrupter tube.

Many problems were discovered during overvoltage insulation tests with the deterioration of these insulation members. Thus, there was found to be electrical breakdown of the throat bushing and creepage paths developing along the surfaces between the throat bushing and the interrupter tube.

It was further found that the mere common practice of rounding oif sharp corners at the resistor contacts was insufficient to modify the high gradient field across adjacent insulation materials.

Some improvement was obtained by applying a conducting coating over the external surface of the throat bushing and connecting this coating electrically to the resistor contacts. However, the discharge of ionized gas and oil through the throat bushing under opening power conditions and resistor current arcs have been found to cause deterioration of the conducting surface on the throat bushing due to tracking of the conducting surface and actual flaking off of the coating.

The principle of the present invention is for the provision of a conductive metallic ring casting which is electrically at the same potential as the resistor contacts, but transfers the field termination to the casting and away from the resistor contacts. This conductive ring surrounds the lower end of the interrupter and is electrically connected to the resistor contacts by a suitable supporting screw connected to the metal support for the resistor tube assembly. Therefore, all of the metallic parts at the lower end of the interrupter tube assembly are at the same potential.

Since the field gradient on the static ring is high, it has been found further advantageous to coat the ring with an insulation material as through the use of the process described in US. Pat. 3,086,888 in the name of Stratton et al., and assigned to the assignee of the present invention, using an insulation material known as Dip-Ite, which is a trade name of the I-T-E Circuit Breaker Company.

Accordingly, a primary object of this invention is to provide a novel conductive shield which encircles the bottom of the interrupter of an oil circuit breaker.

Another object of this invention is to control the high electrical field gradients existing in resistor contacts at the bottom of an interrupter tube which are engageable with the movable interrupter contact.

These and other objects of this invention will become apparent from the following description when taken in connection with the drawings, in which:

FIG. 1 is a cross-sectional view of an interrupter assembly incorporating the novel shield of the invention.

FIG. 2 is a cross-sectional vew of FIG. 1 taken across the section line 22 in FIG. 1, and particularly illustrates the location of the resistor tube assembly.

FIG. 3 is a side cross-sectional View of FIG. 2 taken across the lines 3-3- in FIG. 2.

FIG. 4 is a: top plan view of the novel shield casting used in FIGS. 1, 2 and 3.

FIG. 5 is a cross-sectional view of FIG. 4 taken across the line 5-5 in FIG. 4.

FIG. 6 is a cross-sentional view of FIG. 4 taken across the section line 6-6 in FIG. 4.

Referring first to FIG. 1, I have illustrated therein a typical interrupter structure for an oil circuit breaker which could be made along the lines generally described in the above noted copending application Ser. No. 439,304.

In general, the interrupter is provided with an upper adapter casting 20 which is connectable to a bushing insulator coming into the oil circuit breaker tank within which the interrupter structure is contained. The interrupter structure is then provided with an insulation tube housing 21 which has stationary contacts 22 contained in the upper end thereof electrically connected to casting 20. A plurality of interrupter plates 23 of the usual type are then carried within the interrupter and have a configuration suitable to lead oil and gas flow to suitable exhaust ports 24.

An elongated bayonet contact partially shown in dotted lines in FIG. 1 as bayonet contact 25 is then carried in the usual manner, and passes through the central opening in plates 23 and into contact with stationary contact 22 in order to close the circuit protected by the interrupter. In order to operate the circuit, the elongated contact 25 is moved downwardly and out of the throat bushing 26 at the bottom of the interrupter.

A pluarity of resistor contacts 30 which are contained within a conductive housing 31 are then adapted to be biased into engagement with the sides of bayonet contact 25 as in the interrupter. Resistor contacts of this type are 3 described in detail in the above noted copending application Ser. No. 439,304.

The resistor is typically mounted behind the interrupter of FIG. 1 and can be seen in the sectional drawing of FIG. 2, and the lower portion of the resistor is further shown in FIG. 3.

Thus, the resistor is composed of a plurality of resistance elements which are stacked within a resistor tube 40 and supported by a central support rod 41 in the manner described in the above noted copending application Ser. No. 439,304. The upper end of the resistor is permanently electrically connected to adapter casting 20', while the lower end of the resistor is directly connected to the resistor contact housing 31 with the resistor contacts 30 serving as the resistor termination.

In accordance with the present invention, the resistor contacts 30 are further electrically connected at the bottom of the interrupter to a conductive ring 50, shown in FIG. 1, which may be an aluminum casting which is coated with an epoxy insulation sheath 52.

The conductive ring 50, as best shown in FIG. 1, merges into a casting support section 53 which serves as the lower support for the resistor tube 40 with the lower end of the resistor winding electrically connected to casting portion 53.

Two support and electrical connecting screws 54 and 55, best shown in FIG. 2, then electrically and mechanically connect casting portion 53 and thus ring 50 to the conductive support housing 31 which is electrically connected to the resistor contacts 30. Therefore, the potential of the resistor contacts 30 and the lower end of the resistor structure is connected to the ring 50, with the ring 50 having a suitable circular shape for better distributing the electrical field gradient at the lower end of the resistor contacts when the movable contact 25 is disengaged and removed from resistor contacts 30.

The shield structure is shown in more detail in FIGS. 4, 5 and 6 which show the manner in which the conductive ring section 50 blends into casting section 53 which has an outwardly extending section 60 which serves as the lower support for receiving the bottom of resistor tube 40.

The entire conductive surface of the casting of FIGS. 4, 5 and 6, except for the interior of support section 60 and the upwardly extending section of casting portion 53, is then covered with the insulation coating 52 which further serves as an aid in supporting the high electrical gradients emanating from the casting and toward the remotely located bayonet contact 25 when the contact is moved to its open position. Note that suitable openings 70 and 71 are formed in casting section 53, as shown in FIGS. 5 and 6 for the reception of the screws 54 and 55 which electrically connect the casting to the resistor contacts and mechanically support casting 53.

Although this invention has been described with respect to its preferred embodiments, it should be understood that many variations and modifications will now be obvious to those skilled in the art, and it is preferred, therefore,

that the scope of the invention be limited not by the specific disclosure herein, but only by the appended claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A static shield for an oil circuit breaker interrupter; said interrupter comprising an elongated insulation tube having an upper conductive support; a fixed contact structure connected to said upper conductive support and disposed within the top portion of said insulation tube; interrupter plate means connected in the interior of said insulation tube having a central opening therethrough defining a central clearance passage between the bottom of said insulation tube to said fixed contact structure for an elongated movable contact; sliding resistor contacts connected within the bottom of said insulation tube and adjacent said central clearance passage for slidably engaging an elongated movable contact, and a resistor having a first terminal connected to said fixed contact structure and a second terminal connected to said resistor contacts; said static shield comprising a ring-shaped metallic disk having a solid, symmetric cross section surrounding the exterior of said insulation tube and disposed above the bottom of said insulation tube and electrically connected to said resistor contacts; a throat bushing connected to the interior bottom of said insulation tube and below said resistor contacts; said resistor including a tubular resistor housing physically disposed exteriorly and adjacent said insulation tube and stationarily mounted with respect to said insulation tube; said ring-shaped metallic body having an insulation material cover extending therearound.

2. The device as set forth in claim 1 wherein said ringshaped metallic body has in integral generally flat support cup extending therefrom and lying in a plane perpendicular to the axis of said resistor housing; the bottom of said resistor housing physically disposed in said support cup thereby to physically mount said bottom of said resistor housing with respect to said insulation tube.

3. The device substantially as set forth in claim 2 wherein said integral support cup has an upstanding wall portion extending from the area of connection between said support cup and said ring-shaped body; said upstanding wall portion having screw passages therethrough; said screw passages receiving respective screws extending from said upstanding wall portion, through said insulation tube and into electrical and mechanical connection with said resistor contacts.

References Cited UNITED STATES PATENTS 2,122,281 6/ 1938 Ernanueli 174-21 2,752,459 6/ 1956 Taylor et al. 2,284,603 11/ 1966 Rietz et al.

FOREIGN PATENTS 930,017 7/1963 Great Britain.

ROBERT S. MACON, Primary Examiner 

